What Are Types of Chemical Reactions?

Chemical reactions involve the motion of electrons, leading to the formation and breaking of chemical bonds. There are several different types of chemical reactions. Some common reaction types are:

1. Direct Combination or Synthesis Reaction

In a synthesis reaction two or more chemical species combine to form a more complex product.

The combination of iron and sulfur to form iron (II) sulfide is an example of a synthesis reaction:

8 Fe + S8 --> 8 FeS

2. Chemical Decomposition or Analysis Reaction

In a decomposition reaction a compound is broken into smaller chemical species.

The electrolysis of water into oxygen and hydrogen gas is an example of a decomposition reaction:

2 H2O --> 2 H2 + O2

3. Single Displacement or Substitution Reaction

A substitution or single displacement reaction is characterized by one element being displaced from a compound by another element.

An example of a substitution reaction occurs when zinc combines with hydrochloric acid. The zinc replaces the hydrogen:

Zn + 2 HCl --> ZnCl2 + H2

4. Metathesis or Double Displacement Reaction

In a double displacement or metathesis reaction two compounds exchange bonds or ions in order to form different compounds.

An example of a double displacement reaction occurs between sodium chloride and silver nitrate to form sodium nitrate and silver chloride.

NaCl(aq) + AgNO3(aq) --> NaNO3(aq) + AgCl(s)

5. Acid-Base Reaction

An acid-base reaction is type of double displacement reaction that occurs between an acid and a base. The H+ ion in the acid reacts with the OH- ion in the base to form water and an ionic salt:

The reaction between hydrobromic acid and sodium hydroxide is an example of an acid-base reaction:

HBr + NaOH --> NaBr + H2O

6. Oxidation-Reduction or Redox Reaction

In a redox reaction the oxidation numbers of atoms are changed. Redox reactions may involve the transfer of electrons between chemical species.

As an example, the reaction that occurs when iodide (I2) is reduced to Iodine (I-) and the thiosulfate (S2O32-) is oxidized:

2 S2O32−(aq) + I2(aq) --> S4O62−(aq) + 2 I−(aq)

7. Combustion

Usually in a combustion reaction oxygen combines with another compound to form carbon dioxide and water. An example of a combustion reaction is the burning of naphthalene:

C10H8 + 12 O2 ---> 10 CO2 + 4 H2O

8. Isomerization

In an isomerization reaction, the stuctural arrangement of a compound is changed but its net atomic composition remains the same.

9. Hydrolysis Reaction

A hydrolysis reaction involves water. The general form for a hydrolysis reaction is:

X-(aq) + H2O(l) <--> HX(aq) + OH-(aq)